Is it possible to upload package workbooks to sharepoint site for people without access to the server to view it on the browser? We can't upload the package workbooks to tableau public, and we have only a handful of server user licenses.

While you could save a packaged workbook to SharePoint it would require Tableau Desktop or Tableau Reader to make it usable. It's just an XML file so a web browser would have no idea on what to do with it upon opening it.